With rotary rollers, unlike normally, the object to be lasered moves with it. A big problem here is slippage, which means that the rollers slip under the object and the movement of the object no longer matches the planned movement. The lighter the object, the faster this happens. As a result, you have to pay closer attention to the settings than usual. One should minimize the movements of the roller, if possible. This means that one should use a scan movement along the roller if possible. This way, the laser head is moved back and forth a lot, but the round object is only moved minimally at the end of each path. As described further below, one should possibly also reduce the acceleration of the y-axis, which also reduces the slip. Additionally, you should mainly use the “fill” mode in LightBurn and rather avoid all others (line, offset fill etc.). Furthermore, always use only one pass, not several. It can also help to weigh down the object, i.e. to put a weight in it.
In the LightBurn screenshot above, you can see which settings you should pay special attention to. In the pictures above are examples of favorable and unfavorable movements. Movements along the y-axis should be as small as possible to prevent the object from sliding on the rollers.
- A: The resolution of the lines should be chosen according to the laser spot. Usually for modules up to 10W 0.08 mm or 318 DPI (Lines per Inch), for modules from 20W rather 0.1 mm or 254 DPI. But here you can still play, if lines are visible in the motif, you can reduce the line interval or increase the DPI.
- B: The scan angle should be 0°.
- C: Only one pass should be used.
- D: All objects should be done at once, do not jump between objects.
Another important thing: turn off homing! Homing does not work with a rotary, since the y-axis doesn’t support homing anymore if the rotary is connected (only applies if you use the y-axis for the rotary, but that is the case for 99% of the users in my experience). You don’t need to turn it off in the firmware, but just don’t use it and don’t enable automatic homing at startup. Select “current position” as “start from” option. Never use absolute coordinates.
Acceleration / Speed of the y-axis
If you are struggling with slippage or slipping of the objects, you can try to reduce the speed and especially the acceleration of the y-axis. This will make the axis move more slowly (note: projects also take a little longer) and objects will slip less on the rollers. The firmware parameters for this are:
$111 (Y max rate, max speed in mm/min), Standard usually 6000 $121 (y acceleration, max acceleration in mm/s²), Standard usually 1000
These values can be reduced accordingly. You have to feel your way towards the correct values; you could try a maximum speed of 1000 mm/min and an acceleration of 250 mm/s². If this is not enough, then reduce further.
These values remain stored for the axis, i.e., if the roller is disconnected again, the normal laser will also move as slowly. The values must therefore be reset after using the rotary! If this is too inconvenient, you can make two small LightBurn macros to switch between the modes. Simply right-click on the macro buttons in the console window.
Setting up a rotary
As mentioned in the FAQ section, many people struggle with setting up a rotary to their laser. The top question is: “is this rotary compatible with my laser?” The answer is YES. Not matter which rotary you are trying to connect, as long as it is controlled by a stepper motor (I never saw something else), you can connect it to your laser. The voltage also does not pose a problem. Steppers usually run fine with either 12, 24 or 48V. The only thing that might people think it’s not working, is that sometimes a small change in wiring is required. I will explain this in the next section. First, here is an image of the rotary I used to play around with (Comgrow):
You can either connect this rotary to your existing y-axis motor driver or to the z-axis slot. There are some drawbacks of each method:
- Y-Axis: this one is working without additional hardware. Since the normal y-axis motor is connected to the same port, you need to physically disconnect one of them during operation (or use a switch like presented in the next chapter). You can’t connect both at the same time.
- Z-Axis: the controller board offers another port for a z-axis motor. You could also use this one. Since the Sculpfun board does not contain the stepper driver module for this axis, you need to add one yourself (like this one). Then you have another axis and can control the two motors independently. If you don’t plan to integrate a z-axis, I would recommend using this option because you have less (no) settings to switch between the modes.
Connecting the rotary
Most folks go for the first option. And this is where most people struggle with the setup. I think what they do is to disconnect the y-axis motor plug directly at the motor (not the main board) and attach the rotary motor to that plug. This way, you don’t use the supplied black cable, but only the colored cable that comes out of the motor. That’s because you don’t have any other fitting plugs available. If you did that with the rotary above, this won’t work! If you have a close look at the black cable, you see, that the two middle wires are crossed! And this is required! You now have two options (both of them are fine, it’s just a matter of selection):
- Use the black cable: the only chance to connect this cable is to the motherboard. You need to open the small housing and attach it directly to the y-axis motor port. Luckily, there are two. So, you don’t need to open the box frequently. But you still need to remember to always disconnect one of the motors. (The lower option in the overview picture below)
- Directly connect the colored motor cable to the y-motor plug: in this case, the switching of the two middle wires is not handled by the additional cable. You must change the plug of the rotary motor and switch the two middle wires. It’s a bitt fiddly but using a small needle, you can release the pins from the plug and exchange them. (The top section of the overview image below)
In the next pictures, you can see how to switch the two wires.
Unknown stepper motor
If you have another rotary where you don’t have a fitting cable or don’t know how the motor is wired, you first need to determine which two wires belong together (driving each coil). Here is a video explaining some methods on how to do that:
If you know the two pairs of wires, you need to determine the sequence you have to connect them to the mainboard connector. The Sculpfun boards follow the same sequence for all revisions: 1B 1A 2A 2B (or backwards, depending on the front or back side you are looking at). So, the first two pins go to the first coil, the second pins to the other. If you connected all four wires and the motor stutters, swap the cables of one coil (e.g., swap pin 1 and 2). Then it should work. If the motor turns in the opposite direction as you want it to, just turn the sequence by 180 degrees.
Sculpfun has now released its own roller, which makes it even easier to use. First, no changes need to be made to the steps per mm (they are identical to the normal y-axis), so the green box at the bottom can be ignored. Furthermore, two cables are included, one uncrossed (“Line A”), which can be used to connect the roller directly to the y-motor cable. The second cable, Line B, has the crossed cables, which are necessary if you connect it e.g., to an Ortur laser.
Video on how to connect the Sculpfun roller:
Either way, you should now have a functioning rotary connected to your laser system. The last step is to set it up for use in your laser tool. I’ll show the tool from LightBurn.
There are two ways to properly adjust a rotary:
- Set the steps per millimeter (“steps/mm”) correctly (firmware). The LightBurn assistant is not required and is not activated.
- Via the LightBurn Wizard (software). The firmware “steps/mm” settings are irrelevant.
You do not have to do both! However, you can set both if desired, it does not hurt. The LightBurn assistant is advantageous if the roller requires a different setting for the steps per millimeter than the normal y-axis. In this case, you have to reset the setting every time you change. Here you can use the LightBurn assistant, which then does the conversion itself and is activated with one click. It also allows you to tune the rotation even better.
Setting through steps per mm
[Not required if you use a Sculpfun rotary] Since you switched the motor and driving system, you also need to change the steps / mm value in grbl settings. It is important for grbl to know how many steps per mm this motor/setup uses. You should find this is the documentation of your rotary (the comgrow documentation states 65 steps/mm). You need to set this value for your y-axis (and note down your original value for the y-axis motor!). Furthermore, you might also have to adjust acceleration and speed settings. You can do this either in the device settings window or by typing “$101=65″ in the console window. After you have assured that everything is working, you could also create two macro buttons that switch between rotary and normal operation settings.
If you don’t have any settings supplied with your rotary, you can either attempt to calculate them or guess and trial-and-error set those settings.
Once the setting has been saved, you can start fine-tuning. To accomplish this, measure the rollers and calculate the circumference. For a roll diameter of 10 mm, the circumference would be 31.41 mm (diameter * pi). Draw such a line in LightBurn or LaserGRBL and laser this line with 0% power. The rolls should now rotate exactly 360°. If not, you have to adjust the steps per millimeter setting ($101). The game is repeated until this fits exactly. The value for $101 should be noted or saved in the macro. Now you can switch between normal operation (for Sculpfun $101=80) and rotary operation ($101= the determined value).
Setting via LightBurn assistant
If you don’t want to change the steps per mm every time, you can use the LightBurn wizard. LightBurn then takes over the conversion of the lengths from the motif into the movements of the rotation roller. For this, LightBurn needs two parameters: “mm per rotation” and “Roller Diameter” (A in the following picture). These two values are explained quite simply, but the function is sometimes a bit complicated.
- “Roller Diameter”: is the diameter of the rollers and is simply measured on the hardware.
- “mm per rotation”: this is the slightly more complicated value. This value indicates how many millimeters LightBurn should send to generate a complete rotation of the roller. And here you have to distinguish two cases:
- The steps/mm are set appropriately for the rotary in the firmware: in this case, the value corresponds to the diameter multiplied by pi (i.e., the exact circumference of a roller). Since the steps per mm are correct, a direct relationship is given. So: “mm per rotation = roller diameter * Pi”.
- You do not know the steps/mm, or you do not want to change them every time. Then you have to find out this value by trial and error. You start with a value and click on the test button. LightBurn tries to rotate the rollers 360° back and forth. If the rollers do not rotate far enough, the value must be increased, if it rotates too much, it must be decreased. You do this until you find the right value and the rollers do a perfect 360° turn.
The options are described in the LightBurn documentation, but it is a bit hard to understand there for non-technical users, I guess. As mentioned, when you press Test, the roller rotates the small rollers once 360 degrees. So, the object (that might be lying on it) doesn’t even move all the way around (as long as it is larger than the diameter of the driven rollers).
If you want to check the settings in LightBurn afterwards, it is best to draw a line that is as long as the calculated circumference of the object or roll. If you then let this line be lasered (with 0% power or something like that), then the object or the roll should rotate once by 360 degrees. If it doesn’t quite fit, you have to adjust the parameters accordingly. In LightBurn, you should change the coordinate system to “current position” and not “absolute coordinates” because the coordinates of the rectangular frame do not fit here. If you have limit switches (e.g. S30 series) and a big round object that has more than ~40 cm circumference, you may also need to turn off “soft limits” firmware setting ($20=0).
Additionally, you can enable an “enable rotary” checkbox in LightBurn, so you need just one click to activate the rotary settings.
Here is another video that explains some additional things for the workflow: https://www.youtube.com/watch?v=wL6tXOupQgo (LA Hobby Guy). But the “saving and loading settings” – stuff is not required if you follow my tip using macro buttons.
To clarify the whole thing a little better, here is an example. With the Comgrow Rotary, I can choose between the following settings. The initial situation is as follows: My laser normally has 80 steps per mm in the y-axis; with the roller it is 65 steps per mm and 16 mm diameter of the rollers.
- I leave the steps per mm in the firmware set to 80 (the default setting for a Sculpfun laser). Then I have to use the LightBurn wizard and find out by trial and error what value I need for “mm per rotation”. In this case, I get 40.8 mm per rotation. To use the roller correctly, I have to activate “enable rotary” in LightBurn (so that the values of the wizard become active).
- I change the steps in the firmware to 65. Then I don’t have to use the wizard. If I still want to use it, I have to enter 50.26 mm per revolution there (16 * Pi).
For the mathematicians among you, the value in the first case can also be derived mathematically: 40.8 = 65/80 × 50.26. That is, the ratio of steps per millimeter multiplied by the true circumference of the roll.
Here are some additional explanations to the Sculpfun rotary roller. This one has been designed so that you don’t need to change any settings for the axes (plug and play). Both devices use 80 steps per mm. My rollers of the Sculpfun rotary are 12.8 mm in diameter, which gives a value of 40.25 mm per revolution. In the picture below 12.5 and 40 mm are indicated, you still have to set that exactly for yourself.
Usually, most objects you put on a rotary are not evenly shaped. If it’s just a small difference in diameter, a good approach is to cut a ring from some scratch wood that fits onto the smaller diameter and makes it as wide as the bigger diameter. If you have objects like wine glasses with strong differences in diameter, you can try to design other holders like this: Download (LightBurn file, 3mm thickness):
An even more professional version is shown in this video of Dragoncut:
The file used in the video can be downloaded here.
Calculation of tapered / conical objects to avoid distortion
JoeC297 has created a very nice tutorial at Instructables on how to counteract distortions caused by conical objects. All you have to do is distort the graphic a bit to get the real dimensions you want. You can download a copy of the PDF here.
Rotary – Y-Axis switch / selector
This is just a convenience modification, I wanted to avoid messing with the stepper cables each time I might need to change the Y-axis stepper (nearly exclusively the case if you want to attach a rotary to your laser). I build this switch to easily change between both motors and don’t need to reconnect anything. It’s simply a matter of pushing the switch and the other motor is active. I could not use the z-axis port since I plan to integrate a motorized z-axis to the laser head. I used this switch: Amazon-Link. You can buy a similar fully equipped switch for Sculpfun lasers here (UK).
Standalone rotary laser
Unfortunately, my housing is so small that I can’t raise the laser frame. This leaves me very limited as far as the rotation roller is concerned. Since I had a S9 laser head left in my arsenal, I figured it would be convenient to use it as a standalone rotary laser. The controller is identical to the S6/S9 laser, I used the same main board. The rotation roller is connected as a y-axis, since no other y-axis is used anyway. I can adjust the height via the aluminum profiles.
In addition, an automatically adjustable z-axis is installed here, but it comes from another test and actually has nothing to do with this one.
Update: some new pictures of the final version:
Here are some pictures of the first version (using the z-axis mechanics that is now used here).